Rectifier



Nov. .25, 1947. J. L. FlNcH ETAL RECTIFIER Filed July 7, 1944 r L f k r N H m N d,

muur- PONE 7: .PZNHUDO mbaja .n .mi

.N .muri

m amiiumu no xnju .w .www

iNvENToRs. `JAMES FINCH CLARENCE w. HANsELL..

ATTORNEY Patented Nov. 25, 1947 RECTIFIER James L. Finch, East Rockaway, and Clarence W. Hansell, Port Jefferson, N. Y., assignors to Radio Corporation of America, a corporation of Delaware Application July 7, 1944, Serial No. 543,860

(Cl. 17E-363) 3 claims. 1

This invention relates to improved rectiers, and particularly to polyphase rectifiers and those of the gas filled type.

An object cf this invention is to provide thermionic means for increasing the life of gas filled rectifier tubes.

Another object of this invention is to provide an emcient polyphase rectier system.

A feature of this invention is the use of a nonsinusoidal heating current for the cathodes of a rectifier system.

This invention will best be understood by referring to the accompanying drawing in which:

Fig. 1 is a curve showing the current and magnetic flux in the primary winding and in the core of a transformer for supplying cathode heating current.

Fig. 2 is a curve showing the non-sinusoidal wave form of the voltage impressed on the cathode hegters in the rectifier system of this invention, an Fig. 3 is a curve showing the anode current Wave of the three rectifier tubes, successively. Figures 1, 2 and 3 taken together show the phase relationship between the cathode heating voltage of one rectifier tube and the anode current waves in the three rectifier tubes.

Fig. 4 is a circuit diagram of a polyphase rectier and an output circuit of this invention.

In the past it has been the practice to connect all the cathode heaters in a polyphase rectifier across one phase of the supply. In some particular cases it has been the practice to connect the filament or cathode heater of a particular tube across a particular phase so that the voltage impressed upon it averages as low as possible during the time the plate current is fiowing and so that this voltage reverses during that period. In all such cases the wave form has been essentially sinusoidal, so that very appreciable voltages appear across the filaments during the time anode current flows. This high filament voltage causes the anode current to fiow to one particular portion of the filament during a part of the time and thus causes quicker failure than if the current structure. y

It has been found that the life of hot cathode gas filled rectifier tubes can be increased by the proper choice of the phase angle of the heating 4 current in their cathodes. Our invention lies in the further improvement by the use of a nonsinusoidal voltage for heating the filament or cathode. as indicated by the curves, wherein Fig. 1 indicates the current and magnetic flux fn the were distributed equally over the entire filamentv primary winding and core of a transformer, Fig. 2

shows the wave form of the voltage impressed on l the cathode heater; The wave form according to the system of this invention is so chosen that a minimum of voltage is impressed upon the cathode heater or filament during the time thatthe particular rectifier tube, which we have designated the rectifier 2, in the full line curve of Fig. 3, is carrying plate current as shown. vThe broken lines in Fig. 3 indicate the curve of rectfiers 3 and I. Our invention further lies in the means of obtaining longer tube life by employing this non-sinusoidal wave form. We obtain this Wave form by the use of a special filament transformer which passes beyond the saturation point each half cycle, or by any of the other means known to the art.

Specifically we choose a phase for our filament heating for each rectifier tube I, 2, and 3 in a polyphase system as shown by the circuit diagram Fig. 4, so that the current goes through zero at the middle of the time interval during which this tube is carrying current. We also choose special transformers which, due to the saturation effects, will give a very low output voltage during all or the major portion of this time interval.

Referring, now, in detail to Fig. 4 of the drawing which is a circuit diagram showing the system of this invention: The rectifier system of this invention is shown within the broken line 5. A three phase power line I 0 is shown connected to a rectifier plate transformer I I and a filament heating transformer I2. The primary winding of transformer II is delta connected and the secondary I3 is star or Y-connected to the plate of rectiflers I, 2 and 3. Obviously, of course, the primary may be connected in a Astar connection if yso desired. The center portion of the secondary star connection is shown connected to the negative side of the output I4. The secondary I5 of filament heating transformer I2 is also star connected, the arrangement being such that one side of the filaments of the cathodes of rectifiers I, 2 and 3 are connected to each one of the outside windings of the star connection. The center portion of the star connection is connected to the positive side of the output circuit and also serves asa return circuit for the filament winding. If desired suitable protective resistors (not shown) may be placed across each filament winding.

In the operation of this device when power is supplied from the three phase line I0, the transformer I2 heats the filaments with currents for rectifier tubes I, 2 and 3, as shown by the curves. Each rectifier carries a current for of the power supply cycle giving the resultant group as is shown in Fig. 3 of the drawing.

While we have indicated and described a system of our invention, it will be apparent' to one skilled in the art that our invention is by no means limited to the particular system shown and described, but thatgmany modifications may be made Without departing from the scope of our invention.

What we claim is:

1. In a polyphase alternating current rectifier circuit comprising a plurality of electron discharge devices, each having an anode and a cathode electrode, means for maintaining the cathodes of said electron discharge devices at substantially equal potential throughout the length of operation when a particular tube is carrying anode current, said means including cathode connections to a non-sinusoidal cathode heating current source which is obtained by means of a three .phase transformer operated past its saturation point.

2. A three phase alternating current rectifier circuit comprising a three phase input circuit, three electron discharge devices, each one having an anode and a cathode electrode, means including a cathode transformer of the type with an output wave form which passes beyond the saturation point each half cycle for heating said cathode electrodes, the secondary of said cathode transformer being of the star connection type and having the center portion thereof connected to the positive side of the output of said rectifier circuit, and also to one side of each cathode of said electron discharge device, the outside winding of each star connected coil of said cathode transformer being connected to the other side of a cathode of each electron discharge device, a

separate anode transformer having its primary connected to the same three phase input circuit as said cathode heating transformer and its secondary also being of the star connection type with a center portion thereof connected to the negative side of the output rectifier circuit, and the outside winding'of each star connection coil of said anode transformer being connected to the anode of each one of said electron discharge devices.

3. A rectifier circuit for a plurality of hot cathode gas filled thermionic tubes having at least anode and cathode electrodes, a three phase transformer for heating the cathode electrodes of said thermionic tubes, said transformer being of the type with an output wave form which passes beyond the saturation point of each half cycle, and connections from the output of said transformer to the cathode electrodes of said thermionic tubes, such that the cathodes are maintained at substantially equal potential throughout their length during the period while a particular tube is carrying anode current.

JAMES L. FINCH. CLARENCE W, HANSELL.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,743,238 Robinson Jan. 14, 1930 1,918,173 Bedford July 11, 1933 1,717,581 Prince June 18, 1929 1,740,494 Breisch Dec. 24, 1929 1,612,438 Holst et al Dec. 28, 1926 1,627,707 Latour May 10, 1927 

